Planetary gear train of automatic transmission for vehicle

Abstract

A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting torque of the engine, a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, a first shaft, a second shaft directly connected to the input shaft, a third shaft, a fourth shaft, a fifth shaft selectively connectable to the third shaft, a sixth shaft selectively connectable to the third shaft, a seventh shaft selectively connectable to the fourth shaft, and an eighth shaft selectively connectable to the third shaft, and directly connected to the output shaft.

What is claimed is: 
     
       1. A planetary gear train of an automatic transmission for a vehicle comprising:
 an input shaft receiving torque of an engine; 
 an output shaft outputting torque of the engine; 
 a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element; 
 a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element; 
 a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element; 
 a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element; 
 a first shaft connecting the first rotation element to the fifth rotation element and the ninth rotation element; 
 a second shaft connected to the second rotation element and directly connected to the input shaft; 
 a third shaft connecting the third rotation element to the seventh rotation element; 
 a fourth shaft connected to the fourth rotation element; 
 a fifth shaft connected to the sixth rotation element and selectively connectable to the third shaft; 
 a sixth shaft connecting the eighth rotation element to the twelfth rotation element and selectively connectable to the third shaft; 
 a seventh shaft connected to the tenth rotation element and selectively connectable to the fourth shaft; and 
 an eighth shaft connected to the eleventh rotation element, selectively connectable to the third shaft, and directly connected to the output shaft. 
 
     
     
       2. The planetary gear train of  claim 1 , wherein the first shaft and the fourth shaft are each selectively connectable to a transmission housing. 
     
     
       3. The planetary gear train of  claim 1 , wherein the first rotation element, the second rotation element, and the third rotation element comprise a first sun gear, a first planet carrier, and a first ring gear,
 the fourth rotation element, the fifth rotation element, and the sixth rotation element comprise a second sun gear, a second planet carrier, and a second ring gear, 
 the seventh rotation element, the eighth rotation element, and the ninth rotation element comprise a third sun gear, a third planet carrier, and a third ring gear, and 
 the tenth rotation element, the eleventh rotation element, and the twelfth rotation element comprise a fourth sun gear, a fourth planet carrier, and a fourth ring gear. 
 
     
     
       4. The planetary gear train of  claim 2 , further comprising:
 a first clutch selectively connecting the third shaft to the eighth shaft; 
 a second clutch selectively connecting the third shaft to the fifth shaft; 
 a third clutch selectively connecting the third shaft to the sixth shaft; 
 a fourth clutch selectively connecting the fourth shaft to the seventh shaft; 
 a first brake selectively connecting the first shaft to the transmission housing; and 
 a second brake selectively connecting the fourth shaft to the transmission housing. 
 
     
     
       5. A planetary gear train of an automatic transmission for a vehicle comprising:
 an input shaft receiving torque of an engine; 
 an output shaft outputting torque; 
 a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element; 
 a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element; 
 a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element; and 
 a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element, 
 wherein the input shaft is directly connected to the second rotation element, 
 the output shaft is directly connected to the eleventh rotation element, 
 the first rotation element is directly connected to the fifth rotation element and the ninth rotation element, 
 the third rotation element is directly connected to the seventh rotation element, 
 the sixth rotation element is selectively connectable to the third rotation element, 
 the eighth rotation element is directly connected to the twelfth rotation element and selectively connectable to the seventh rotation element, 
 the tenth rotation element is selectively connectable to the fourth rotation element, and 
 the eleventh rotation element is selectively connectable to the third rotation element. 
 
     
     
       6. The planetary gear train of  claim 5 , wherein the first rotation element and the fourth rotation element are each selectively connectable to a transmission housing. 
     
     
       7. The planetary gear train of  claim 5 ,
 wherein the first rotation element, the second rotation element, and the third rotation element comprise a first sun gear, a first planet carrier, and a first ring gear, 
 the fourth rotation element, the fifth rotation element, and the sixth rotation element comprise a second sun gear, a second planet carrier, and a second ring gear, 
 the seventh rotation element, the eighth rotation element, and the ninth rotation element comprise a third sun gear, a third planet carrier, and a third ring gear, and 
 the tenth rotation element, the eleventh rotation element, and the twelfth rotation element comprise a fourth sun gear, a fourth planet carrier, and a fourth ring gear. 
 
     
     
       8. The planetary gear train of  claim 6 , further comprising:
 a first clutch selectively connecting the seventh rotation element to the eleventh rotation element; 
 a second clutch selectively connecting the third rotation element to the sixth rotation element; 
 a third clutch selectively connecting the seventh rotation element to the eighth rotation element; 
 a fourth clutch selectively connecting the fourth rotation element to the tenth rotation element; 
 a first brake selectively connecting the first rotation element to the transmission housing; and 
 a second brake selectively connecting the fourth rotation element to the transmission housing. 
 
     
     
       9. The planetary gear train of  claim 8 , wherein speed stages implemented by selectively operating the first, second, third and fourth clutches and the first and second brakes include:
 a first forward speed stage, implemented by operating the first brake and the third and fourth clutches; 
 a second forward speed stage, implemented by operating the first and second brakes, and the fourth clutch; 
 a third forward speed stage, implemented by operating the second brake and the third and fourth clutches; 
 a fourth forward speed stage, implemented by operating the second brake and the second and fourth clutches; 
 a fifth forward speed stage, implemented by operating the second brake and the first and fourth clutches; 
 a sixth forward speed stage, implemented by operating the first, second, and fourth clutches; 
 a seventh forward speed stage, implemented by operating the second brake and the first and second clutches; 
 an eighth forward speed stage, implemented by operating the second brake and the first and third clutches; 
 a ninth forward speed stage, implemented by operating the first brake and the first and third clutches; and 
 a reverse-speed stage, implemented by operating the first brake and the second and fourth clutches.